Solvent extraction method



July14, 1970 J. c. GATSIS SOLVENT EXTRACTION METHOD 2 Sheets-Sheet 1Filed March 29, 1968 ES QE sta w ub v 59;

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%ZM74 ATTORNEYS 3 \ssu mm Jul 14, 1970 Filed March 29, 1968 fases if J.G. GATSIS 3,520,794

SOLVENT EXTRACTION METHOD 2 Sheets-Sheet 2 Coal Efacf v M m t tt i 0 l mk g I f g N x 3 E, L Ls F N a r B 8 9.) k a P1 //v vnvron- John 6.Gafs/s Lk BY- ATTORNEYS I United States Patent 3,520,794 SOLVENTEXTRACTION METHOD John G. Gatsis, Des Plaines, Ill., assignor toUniversal Oil Products Company, Des Plaines, 111., a corporation ofDelaware Filed Mar. 29, 1968, Ser. No. 723,341 Int. Cl. C10g 1/00 US.Cl. 208-8 Claims ABSTRACT OF THE DISCLOSURE Method and apparatus forliquefying coal via solvent extraction. Coal and solvent are introducedinto the tubes via a vertical shell and tube extraction zone. The tubeis perforated in such a manner that coal extracted may be removedthrough the perforations into the shell side with the remaining solidmaterial being removed from the tubes. Hydrocarbons useful as fuel and/or chemicals may be obtained from the liquid coal extract.

BACKGROUND OF THE INVENTION This invention relates to a solventextraction method. It also relates to a method for liquefying coal usinga selective solvent. It particularly relates to a method for liquefyingcoal utilizing a novel extraction zone design.

It has long been known that hydrocarbon gases, liquids, pitch, and thechemicals derived from or allied to these hydrocarbons may be obtainedin some form from coal which is mined from the earth. Usually, the priorart has employed destructive distillation or other gasificationprocesses for the conversion of coal into these more valuable and usefulproducts. Recently, the prior art has developed a high pressurehydrogenation of coal technique to effectuate such conversion. Stillmore recently, methods involving solvent extraction techniques have beenperfected by the prior art for obtaining useful fuels and chemicals fromcoal wherein the crushed coal is contacted with a selective solventwhich acts as a hydrogen-donor for supplying sufiicient hydrogen to thecoal to aid in converting it to a liquid phase. Following the solventextraction step, the prior art schemes have generally utilized variousproduce recovery procedures, such as hydrogenation of the liquid coalextract, for increasing its value and utility together with retorting orcoking of the residual materials obtained from the solvent extractionstep to still further convert these coal derived priducts into moreuseful and valuable products.

One of the main difficulties in the liquefaction of coal using thesolvent extraction process is in the separation step followingextraction, i.e., the separation of the undissolved coal and inorganicmaterial from the liquid. The prior art has attempted to make thisseparation by filtration methods using a precoated filter attemperatures which approach atmospheric temperatures. However, the priorart methods of separating the insoluble material from the liquid coalextract have been, for the most part, unsatisfactory in the commercialsense.

Since it is clear to those skilled in the art that the vast mineralreserves of bituminous coal represent an extreme ly important supply ofenergy, it would be desirable to improve upon the prior art processes,particularly the solvent extraction process in order to reduce the costof obtaining typical petroleum-type products from coal.

SUMMARY OF THE INVENTION Therefore, it is an object if this invention toprovide a method for the liquefaction of coal whereby valuablehydrocarbon products may be obtained therefrom.

It is a specific object of this invention to provide an ice improvedmethod for subjecting pulverized coal to solvent extraction usingsolvent which is selective for dissolving the coal, e.g., Tetralin.

It is another specific object of this invention to provide an improvedmethod for liquefying coal via solvent extraction whereby increasedefliciency of the separation step is significantly increased in a facileand economical manner.

This invention has both apparatus and method aspects. In accordance withthe practice of one embodiment of the apparatus aspect, there isprovided apparatus which comprises in combination a vertically disposedenclosed shell having at least one conduit extending through said shellin parallel relationship with the vertical axis of said shell, means forintroducing a mixture of solid and liquid materials into the lower endof said conduit, first outlet means for removing solid material from theupper end of said conduit, perforate means in the upper section of saidconduit providing a passageway for liquid between said con duit and saidshell, and second outlet means for withdrawing liquid from said shell.

A specific embodiment of the apparatus aspect includes the apparatushereinabove wherein said perforations comprise orifice openings having asmall enough diameter to prevent the passage therethrough of solidparticles having an average diameter of five (5) microns or larger.

Further, in accordance with the practice of one method embodiment ofthis invention, there is provided a method for liquefying coal whichcomprises passing granular coal and solvent into the lower end of anextraction zone maintained under coal extraction conditions; said zonecomprising at least one vertically disposed conduit having animperforate lower section and perforate upper section; withdrawingliquefied coal from said upper section through the perforations thereinwhile retaining solid material within said conduit; and removing solidmaterial from the upper end of said conduit.

In a specific method embodiment of the present invention there isprovided a method for liquefying coal which comprises contactinggranular coal with a solvent selective for coal in the lower end of atleast one smaller conduit disposed concentrically in a larger conduit,passing the coal and solvent upwardly through said smaller conduit undercoal extraction conditions; withdrawing liquefied coal and solventthrough at least one opening in the upper section of said smallerconduit into the larger conduit in a manner such that solid material issubstantially retained in said smaller conduit; removing liquefied coaland solvent from said larger conduit; and, removing solid material fromthe upper end of said smaller conduit.

In other words, the method of the present invention utilizes a reactorconsisting of two concentric tubes with the upper section of the innertube consisting of a perforated or filter element. In operation, theground coal is mixed with the solvent and the mixture is passed upwardlyin the reactor through the inner tube. Preferably, a temperaturegradient is applied across the reaction or liquefying zone with thetemperature increasing from the bottom of the inner tube to the top ofthe tube. As the coal proceeds upwardly through the liquefaction zone,the coal is dissolved into the solvent and as it proceeds through theperforated section of the inner tube the liquid will pass through thefilter and the unreacted coal passed upwardly and out of the extractionzone.

DESCRIPTION OF THE INVENTION The coal preferred for use in the practiceof the present inventive method is of the bituminous type such asPittsburgh seam coal. More preferably, however, the bituminous coal is ahigh volatile content coal having a volatile content greater than about20% by weight of 1m.a.f. coal (moisture and ash-free coal).

The extraction of coal by means of solvent has been described (bydefinition) as a partial conversion of the coal since not only is thecoal reacted with the hydrogen which is transferred from the solvent,but there is also a solution phenomenum which actually dissolves thecoal which has accepted the hydrogen from some source into the solventliquid phase. Therefore, as used herein, the term liquid coal extract,liquefied coal fraction, liquefied coal, or other words of similarimport, is intended to include the liquid product which is obtained fromthe solvent extraction of the coal with the selective solvent and,generally, will be described on the basis of being solvent-free eventhough a portion of the liquid coal extract comprises hydrocarbonssuitable for use as the selective solvent. The practice of the presentinvention is performed under conditions which increase the kinetics ofthe reaction while maintaining the components therein primarily liquidphase; although, in some cases it may be desirable to practice thisinvention in the presence of a vaporized solvent by using a gaseousextraction technique.

Suitable solvents for use in the practice of this invention are thosewhich are of the hydrogen-donor type and are at least partiallyhydrogenated and include naphthalenic hydrocarbons. Other aromatic typehydrocarbons are suitable if an extraneous source of hydrogen isprovided. Preferably, the solvent is one which is in liquid phase at therecommended temperature and pressure for the extraction and/orpulverization step. Mixtures of hydrocarbons are generally employed andpreferably are derived from intermediate or final products obtained fromsubsequent processing following the practice of this invention.Typically, these solvent hydrocarbons or mixtures of hydrocarbons boilbetween about 260 C. and 425 C. Examples of suitable solvents aretetrahydronaphthalene (Tetrahn), Decalin, biphenyl, methylnaphthalene,dimethylnaphthalene, etc. Other types of solvents which may be added tothe preferred solvents of this invention for special reasons includephenolic compounds, such as phenols, cresols, and xylenols. It is alsoto be recognized that it some cases it may be desirable during asubsequent separation step prior to the removal of the solvent from theliquid coal extract to add an antisolvent, such as saturated paraflinichydrocarbon like hexane, to aid in the precipitation of tarry and solidresidue from the coal extract of the invention.

However, in the selection of a suitable solvent it must be recognizedthat unless hydrogen is added to the extraction zone the solvent musthave the ability to transfer hydrogen to the pulverized coal during theextract step. In other words, in the absence of added hydrogen, it is arequirement of this invention that the rich solvent leaving theextraction zone having liquid coal extract dissolved therein has areduced hydrogen content compared to the hydrogen content of the leansolvent which is added to the extraction zone in admixture with thefeed.

A particularly preferred embodiment of this invention includes the useof the selective solvent during the pulverization step wherebyrelatively coarse size coal is reduced to granular coal of optimum sizefor extraction. This preferred embodiment is predicated on the theorythat having the presence of a hydrogen-rich solvent during thepulverization step of the coal results in a substantial increase in theefficiency of the operation and in many cases results in a decreased useof solvent for obtaining the same amount of liquid coal extract.

With respect to the benefit gained from having the solvent presentduring the pulverization step, it is believed that at the point of shearfor the crushing and grinding of the coal the shear site is extremelyreactive and hydrogen, therefore, can be transfercd into that site moreeasily then if the coal is pulverized prior to contact with the solvent.In addition, the small particles of coal which are sheared away from alarge lump immediately expose not only the highly reactive shear site tothe solvent, but also exposes an extremely large surface area to thesolvent, thereby enabling the small particles of coal to almostimmediately dissolve in the solvent and become a part of the liquid coalextract. While not desiring to be limited by this theory, the practiceof this preferred embodiment of the invention is at least explained tothose skilled in the art so that future work may be used along theselines to further improve upon the inventive concepts contained herein.

Apparatus for use in pulverizing the lump or coarse coal feed aspracticed in the present invention may be any type known to thoseskilled in the art. Conventional ball mills or rod mills may be usedwith satisfactory results. Preferably, the apparatus must be able topulverize lump or coarse coal in the presence of significant quantitiesof liquid solvent without difficulty. Those skilled in the art arefamiliar with the kinds of apparatus for processing wet solids and thecrushing and grinding thereof, such that no detailed discussion of theapparatus need be presented herein. The primary requirement for crushingand grinding of the lump coal is that coarse coal usually having anaverage particle diameter in excess of 0.08 inch and, typically, about0.25 to 2.0 inches must be processed thereto and reduced in size to anaverage particle diameter which would be of at least a 8 Tyler screensize and, preferably, would be reduced to an average particle size for14 Tyler screen size. As used herein the term Tyler screen refers in allinstances to the commercial Tyler Standard Screens. The correlationbetween Tyler screen mesh and average particle diameter is as follows:

Tyler screen mesh-Average diameter of particles D in.

The conditions during the pulverization step may be varied widelyaccording to the desires of those skilled in the art and practicing thisinvention. The temperature, of course, may be varied over a relativelybroad range, from essentially atmospheric temperature to a relativelyhigh temperature. It is distinctly preferred in the practice of thisinvention that the temperature of the coal and the solvent be maintainedat a relatively high temperature, say, from 300 C. to 500 C. Thepressure, in similar manner, may be varied over an extremely wide rangefrom atmospheric pressure to, say, 10,000 p.s.i.g. with a preferredpressure being about p.s.i.g. or, typically, about 70 p.s.i.g.

The operation of the pulverization equipment is preferably performed sothat the oversized material; that is, greater in size than the 8 Tylerscreen size, be separated and returned to the apparatus for furtherpulverization. The utilization of the closed circuit technique is wellknown to those skilled in the art and is preferred in the practice ofthis invention. Unless otherwise stated, closed circuit operation of thepulverization equipment will be deemed inherent in the practice of thisinvention.

The amount of solvent which is used in the present invention generallywill range from 0.2 to 10 pounds of solvent per pound of coal.Satisfactory results may be obtained in utilizing approximately equalamounts of solvent to coal on a weight basis. In the practice of thepreferred embodiment of this invention, the conditions during thepulverization step should be chosen such that the coarse coal is reducedin size to at least a -8 Tyler screen size and the solvent has a chanceto react and dissolve the coal to an extent such that the coal particlesare at least partially dissolved in the solvent. As more fully developedhereinbelow, the conditions are chosen in the pulverization step suchthat from 10% to 40% of the m.a.f. coal is dissolved in the solvent withat least an additional 50% by weight being dissolved during thesubsequent digestion zone.

Following the size reduction step wherein at least part of the coal hasbeen dissolved in the solvent and oversized solid materials have beenseparated, the effluent product comprising solvent having dissolvedtherein liquid coal extract and undissolved solid coal is passed intothe concentric tube a digestion zone which is a reaction zone of thepresent invention for the substantial conversion of the coal into liquidcoal extract. The operating conditions for the digestion zone include atemperature from 300 C. to 500 C., a pressure from atmospheric to 10,000p.s.i.g., a solvent to coal weight ratio from 0.2 to 10, and a residencetime from 30 seconds to 5 hours, suflicient to dissolve coal such that atotal in excess of 50% by weight of m.a.f. coal has been liquefied. Itis to be noted that the temperature and pressure conditions during thedigestion zone may be the same, may be higher, may be lower, or may beany different configuration desired by those skilled in the art overthose conditions maintained in the pulverizatipn zone. It has been foundsatisfactory in the practice of this invention that the temperature andpressure in the digestion zone be maintained essentially at the samelevel as the temperature and pressure maintained in the pulverizationzone. Additionally, it has been found that significant efficiencies ofoperation of the concentric tube digestion zone may be obtained byimposing an increasing temperature gradient across the digestion zone.In other words, the lower end of the inner tube should be maintained ata relatively low temperature whereas the withdrawal of the liquidextract through the perforations in the upper section of the tube shouldbe at a relatively high temperature. Preferably, the relatively lowtemperature in the lower section of the tube should be from 350 C. to400 C., preferably, 380 C. and the relatively high temperature at theupper section of the tube should be from 400 C. to 500 C., typically,430 C.

Since the purpose of the digestion zone, including in the preferredembodiment the pulverization and the digestion zones, is tosubstantially complete the conversion of the coal into a liquid coalextract, it may be desirable to add to the digestion zone additionalsolvent, add a hy drogen-containing gas to the digestion zone, and/orutilize a catalyst in the digestion zone. The catalyst used may beconventional, may be homogenous or heterogenous and may be introduced inthe pulverization zone and/ or digestion zone in admixture with theliquid solvent or with the solid coal. Those skilled in the art, from aknowledge of the characteristics of the coal, solvent and the propertiesdesired for the end product will know whether or not it may be desirableto use any or all of these desirable features in the digestion zone.Conventional hydrogenation catalyst may be desirable, such as palladiumon an alumina support or a cobalt-molybdate catalyst or any otherhydrogenation catalyst known to those skilled in the art and applicableto the solventcoal system environment maintained in the digestion zoneincluding the use of a slurry-catalyst system. Hydrogenation in thedigestion zone generally accomplishes the following functions: transferof hydrogen directly to coal molecules; transfer of hydrogen to hydrogendonor molecules; transfer of hydrogen from hydrogen donor molecules tocoal molecules; and, combinations of above. Homogenous catalysts may beintroduced with the coal, or hydrogen donor compounds, in thepulverization step of the digestion zone. Examples of catalysts suitableinclude compounds containing tin, nickel, molybdenum,

tungsten, and cobalt. By way of emphasis, as used herein, the termextraction zone is intended to include the pulverization step, thedigestion step, or the combined pulverization-digestion step.

After separation of the solvent and undissolved coal residue (andcatalyst, if any) from the total effluent of the digestion zone, theliquid coal extract is further processed by means known to those skilledin the art, such as conventional hydrogenation treatment to convert theliquid coal extract into more valuable products, such as fuel, e.g.,gasoline boiling range products and/or chemicals, such as aromatichydrocarbons, the utility of which is well known. The invention may bemore fully understood with reference to FIG. 1 and FIG. 2 which aredetailed schematic representations of apparatus for practicing thepresent invention.

DESCRIPTION OF THE DRAWINGS Referring now to FIG. 1, coarse coal havingan average particle diameter generally in excess of 0.08 inch isintroduced into the system via line 10. A suitable selective solventenriched in hydrogen content is introduced into admixture with thecoarse coal from line 11, the source of which is more fully discussedhereinafter. As previously mentioned, the oversized solid material fromthe pulverization zone is also preferably returned to the pulverizationzone via line 12. The entire admixture of coarse coal and solvent ispassed via line 13 anto mill 14 which conventionally may be of the ballmill type.

Suitable pulverization conditions including a temperature of about 380C., a pressure of about 70 p.s.i.g., and a solvent to coal weight ratioof about 1 is maintained in mill 14 such that the coarse coal is reducedto an average particle diameter between 0.08 inch and 0.04 inch and atleast a portion of the coal, say, about 17% by weight is dissolved intothe solvent.

The effluent from mill 14 containing solvent having dissolved thereinthe liquid coal extract, undissolved coal of proper small particle size,and undissolved coal of oversize is passed via line 15 into separator 16which may be of the cyclone type. Conditions are maintained in separator16 whereby the oversized coal particles, preferably, in admixture withat least a portion of the liquid material is removed via line 12 andreturned to mill 14 in a manner previously discussed.

The solvent having dissolved therein the liquid coal extract plusundissolved pulverized coal (and insoluble inorganic material) is passedvia line 17 into digestion zone 19 which contains concentric tube 22placed in shell 33. Inner tube 22 contains perforations 23 which arejust large enough to allow the passage of liquid therethrough whileprohibiting the passage of any substantial amounts of solid materialtherethrough. Added solvent, if any, may be introduced into the systemvia line 18 in an amount sufficient to maintain the solvent-coal ratioat the desired level and/ or to maintain the hydrogen content of thesolvent present in digestor 19 at a sufficiently high level.Furthermore, catalyst (from means not shown) may be advantageously usedin the digestion and/ or extraction step. The material in inner tube 22passes upwardly until it reaches the perforation zone 23 wherein liquidcoal extract plus solvent pass through the perforations into the shell33 of digestor 19. Since the operation is continuous, the retained solidmaterial wet with solvent and oil is removed from digestor 19 via line21. Typically, the solid material removed from line 21 may contain from25% to 50% by weight liquid. In any event, at least by volume of theliquid material is passed into shell 33. As previously mentioned, ifdesired, by means not shown an antisolvent, such as a light hydrocarbonof the hexane type, may be added into the inner tube 22 at a locationclose to perforation zone 23 in an effort to further aid in removingtars and solid materials from the desired solvent and liquid coalextract. If an antisolvent is used, then, of course, the material in theshell 33 also will contain such light hydrocarbon.

The liquid coal extract plus solvent is passed out of shell 33 via line20 into fractionation zone 24 which may be of a conventionaldistillation column type. Suitable conditions are maintained thereinsuch that a distillate fraction comprising light hydrocarbons may bewithdrawn via line 26 and the liquid coal extract may be removed vialine 25 for further processing in accordance with the practices known tothose skilled in the art, including hydrogenation techniques forupgrading the liquid coal extract to the desired valuable products ofmotor fuel and/or chemicals. Means (not necessarily shown) for removingthe antisolvent, if any, may be also incorporated broadly intofractionation zone 24.

In the practice of the present invention, a material suitable in boilingrange, in characteristics as a selective solvent for the coal, iswithdrawn from fractionation zone 24 via line 27 and, in a preferredembodiment of this invention, passed into hydrogenation zone 29.Hydrogen is introduced into hydrotreater 29 through conduit 30 to supplythe required hydrogen. Generally, this hydrotreating step may be carriedout by any means known to those skilled in the art of hydrotreating. Thepurpose of the hydrogenation zone is to restore hydrogen balance to thesolvent in order to maintain efliciency of extraction both in thepulverization step and digestion step previously discussed. Preferably,hydrotreating catalyst is loaded into a fixed bed, not shown, withinreaction zone 29. The material in line 27 is mixed with fresh hydrogenfrom line 30, by means not shown, and recycle gas from a source notshown, heated and passed at once through the fixed bed of catalyst. Ahydrotreated efiluent is withdrawn from the reaction zone and cooled andintroduced into a separator, all by means not shown. The efiluent isseparated into a normally hydrotreated product and a normally gaseousstream. As those in the art are familiar, the normally gaseous streamcontaining hydrogen is recycled to the reaction zone by means not shown.The

normally liquid product stream may be fractionated or stripped to removedissolved gases, such as hydrogen or hydrogen sulfide or, if desired,this step may be omitted.

By way of emphasis, it is to be noted that the sequence of steps andequipment required for hydrogenation is well known to those skilled inthe art and has not been shown in the drawing; rather, all steps andequipment necessary for practicing hydrogenation are embodied in the boxshown as hydrogenation zone 29 in the drawing.

The hydrogenation catalyst is preferably sulfur resistant and comprisesa silica-alumina support having at least one metal or metal compound ofGroup VI of the Periodic Table and one metal or metal compound of GroupVIII of the Periodic Table. Especially preferable in the practice ofthis invention are those hydrogenation catalysts having tungsten and/ormolybdenum along with nickel and/or cobalt on silica-alumina supports.Other supports such as alumina, silica-zirconia, silica-magnesia,faujasite, mordenite, inorganic oxide matrix containing at least onecrystalline aluminosilicate, etc., are also suitable. Other metals whichare also satisfactory include the noble metals such as platinum orpalladium. These latter noble metal catalysts are generally satisfactorywithout the presence of a Group VIII metal.

The hydrotreating conditions employed in hydrogenation zone 29 areselected to convert the solvent separated from the eflluent of theextraction zone to a product having increased hydrogen content. Suitablepressure ranges are from about 400 p.s.i.g. to about 2,000 p.s.i.g.,preferably, from 600 p.s.i.g. to 900 p.s.i.g. Suitable liquid hourlyspace velocity by weight (LHSV) is from about 0.5 to about 20,preferably, from 3 to 10. The hydrogen-to-oil mole ratio may be from 2to 20, preferably, from to 15. Typically, the temperature will be in therange from 232 C. to about 454 C.

The properly hydrogen enriched solvent stream is removed fromhydrogenation zone 29 via line 31 and returned to the digestion zone vialine 11 and/or line 1 8, as previously mentioned. Additional suitablesolvent, if necessary, may be added to the system from a source notshown via line 32. In addition, for control purposes a by-pass ofsolvent material around hydrogenation zone 29 may be accomplished bymeans of line 28. Normally, a small amount of material will always beflowing in line 28 so as to provide flexibility of control on thehydrogen content of the material flowing in line 31.

As previously mentioned, it may be highly desirable to add hydrogen gasand a catalyst to digestion zone 19. The means by which such materialsmay be additionally added to digestor 19 have not been shown since thoseskilled in the art from general knowledge and the teachings presentedherein would know how to add these further improvements to the inventivemethod of the present invention.

Referring now to FIG. 2, there is shown an apparatus in combinationwhich comprises a vertically disposed shell 33 having at least oneconduit 22 extending through the shell in concentric fashion. Means forintroducing liquids and solids into the inner tube 22 via line 17 can beby any means known to those skilled in the art. One such means would bea screw conveyor which would carry the feed material through the filtersection 23, would compress the solids in the filter section, therebyforcing the liquid through the holes in zone 23 into the space 37 ofshell 33. Another method of reaching the same result would be to have ahigher pressure in tube 22 than is maintained in space 37. Additionally,the apparatus includes outlet means 21 for withdrawing solid materialfrom the inner tube 22 and outlet means 20 for removing liquid fromshell 33.

In addition, there is shown inlet means 34 for introducing hydrogen gasinto admixture with the feed material in line 17 and additional outletmeans 38 located in the upper section of shell 33 to remove gaseousmaterials from the eflluent which passed through perforations 23 intospace 37.

In operation, pulverized coal including solvent and catalyst, ifdesired, is passed via line 17 as a slurry into the lower end of innertube 22. Hydrogen gas may also be introduced with the feed material vialine 34. The entire mixture passes upwardly through inner tube 22 untilit reaches filtration zone 23 containing a series of orifice openingshaving a small enough diameter to prevent the passage through of solidmaterials having an average diameter of five (5) microns or larger.

The liquid coal extract plus solvent, hydrogen gases, and other lightgases pass through the perforations in zone 23 into space 37 of shell33. The insoluble material comprising inorganic material, such as ash,plus any undissolved coal pass out of the system from inner tube 22 vialine 21. The material which has passed through filtration zone 23 intospace 37 of shell 33 is separated therein with the gaseous materialsbeing removed from shell 33 via line 35. The accumulated liquid coalextract plus solvent is withdrawn from shell 33 via line 20. If desired,a portion of the liquid coal extract may be returned to the digestionzone via line 35. In addition, should there be a significant quantity ofundissolved coal in the solid material being removed via line 21, aportion thereof may be returned to the extraction step via line 36.

It is to be noted that the digestion zone comprising shell 33 and tube22 is, in effect, of well known shell and tube design. The embodimentsof the present invention include the use of at least one tube 22 withinshell 33, but may include a plurality of tubes 22 depending upon thedesign parameters utilized by those skilled in the art. A typicalcommercial configuration would include a shell having a diameter ofeight (8) feet and containing 1,000 to 5,000, typically, 4,000 tubes 22of 2 to 3 inches in diameter. The perforations in zone 23 of tube 22 maybe placed in any manner desired by those skilled in the art. It isdistinctly preferred, however, that the perforated area of tube 22 occurover less than 75% of the length of the conduit. However, theperforations may occur over any portion of tube 22 with the preferredarrangement being that all of the perforations be contained in the upperone-half of tube 22. The diameters of the holes or orifices may rangefrom five microns to .093 inch in diameter sufiicient to prevent thepassage therethrough of any significant amount of solid material. Thegeometry of the hole spacing is not critical in the practice of thisinvention.

PREFERRED EMBODIMENT A preferred embodiment of the invention includes amethod for liquefying coal which comprises the steps of: (a) admixingcoarse size bituminous coal with solvent selective for dissolving coal;(-b) introducing the solventcoarse coal admixture into a pulverizationzone under conditions including a temperature from 300 C. to 500 C.,pressure from atmospheric to 10,000 p.s.i.g., solvent to coal ratio from0.2. to sufficient to reduce said coarse coal to at least a 8 Tylerscreen size and to partially dissolve coal into said solvent; (c)passing the pulverized coal-solvent product including dissolved coal ata relatively low temperature into the lower end of at least one smallerconduit disposed concentrically in a larger conduit; (d) passing saidcoal-solvent product upwardly through said smaller conduit underdigestion conditions including a temperature from 300 C. to 500 C.pressure from atmospheric to 10,000 p.s.i.g., solvent to coal weightratio from 0.2 to 10, and a residence time from seconds to 5 hourssufficient to dissolve coal such that a total in excess of 50% by weightof m.a.f. coal is liquefied as liquid coal extract; (e) Withdrawing saidliquid coal extract at a relatively high temperature through at leastone opening in the upper section of said smaller conduit into the largerconduit such that solid material is substantially retained in saidsmaller conduit; (f) removing solid material from the upper end of saidsmaller conduit; and (g) recovering liquid coal extract from said largerconduit.

Another preferred embodiment of the present invention includes themethod hereinabove wherein said digestion conditions include thepresence of hydrogen gas and still further includes the presence of acatalyst.

I claim:

1. Method for liquefying coal which comprises the steps of:

(a) admixing coarse size bituminous coal with solvent selective fordissolving coal;

(b) introducing the solvent-coarse coal admixture into a pulverizationzone under conditions including a temperature from- 300 to 500 0,pressure from atmospheric to 10,000 p.s.i.g., solvent to coal ratio from0.2 to 10 suificient to reduce said coarse coal to at least a 8 Tylerscreen size and to partially dissolve coal into said solvent;

(0) passing the pulverized coal-solvent product including dissolved coalat a relatively low temperature into the lower end of at least onesmaller conduit disposed concentrically in a larger conduit;

(d) passing said coal-solvent product upwardly through said smallerconduit under digestion conditions including a temperature from 300 C.to 500 C., pressure from atmospheric to 10,000 p.s.i.g., solvent to coalweight ratio from 0.2 to 10, and a residence time from 30 seconds to 5hours suflicient to dissolve coal such that a total in excess of 50% byweight of m.a.f. coal is liquefied as liquid coal extract;

(e) withdrawing said liquid coal extract at a relatively hightemperature through at least one opening in the upper section of saidsmaller conduit into the larger conduit such that solid material issubstantially retained in said smaller conduit;

(f) removing solid material from the upper end of said smaller conduit;and

(g) recovering liquid coal extract from said larger conduit.

2. Method according to claim 1 wherein said digestion conditions includethe presence of hydrogen gas.

3. Method according to claim 2 wherein said digestion conditions includethe presence of a hydrogenation catalyst.

4. Apparatus comprising in combination: a vertically disposed, enclosedshell having at least one conduit extending through said shell inparallel relationship with the vertical axis of said shell, means forintroducing a mixture of solid and liquid materials into the lower endof said conduit, first outlet means for removing solid material from theupper end of said conduit, perforate means in the upper section of saidconduit occurring over less than of the length of said conduit providinga passageway for liquid between said conduit and said shell, and secondoutlet means for withdrawing liquid from said shell.

5. Apparatus according to claim 4 wherein said perforations compriseorifice openings having a small enough diameter to prevent the passagetherethrough of solid particles having an average diameter of five (5)microns or larger.

References Cited UNITED STATES PATENTS 2,595,979 5/1952 Pevere et a1.2088 2,453,633 11/1948 Logan 19614.52

769,531 9/1904 Bremer 202-254 2,851,396 9/1958 Myers 19614.52

690,693 1/1902 Von Boyen 2088 2,885,337 5/1959 Keith et a1. 20882,784,148 3/1957 Edmonds et a1. 2088 DELBERT E. GANTZ, Primary ExaminerV. OKEEFE, Assistant Examiner US. 'Cl. X.R.

